This Week's Sky at a Glance, August 29 – September 7

FRIDAY, AUGUST 29

■ Saturn is the brightest dot low in the east right after dark. But as the evening advances, Saturn gets competition. Fomalhaut, the Autumn Star, makes its appearance above the southeast horizon some three fists to Saturn's lower right.

Its rising time will depend on where you live. But by 11 p.m. now, you should have no trouble identifying Fomalhaut sparkling low in the southeast if you have a good view in that direction. No other 1st-magnitude star is anywhere near there.

Saturn and Fomalhaut are magnitudes +0.7 and +1.2, respectively. Can you see that the star twinkles and the planet doesn't?

■ As dawn brightens this week, Jupiter, Venus, and low Mercury form a tall, straight line in the east as shown below.

SATURDAY, AUGUST 30

■ First-quarter Moon (exactly so at 2:25 a.m. EDT tonight). The Moon shines in the southwest right after nightfall, in the head of Scorpius. Look for orange Antares about 5° to the Moon's upper left (for North America). Delta Scorpii, the second-brightest star in the area, is a similar distance to the Moon's upper right.

SUNDAY, AUGUST 31

■ Now Antares and Delta Scorpii line up to the right of the Moon. The line points the same length the other way from the Moon to the spout of the Sagittarius Teapot.

MONDAY, SEPTEMBER 1

■ September's arrival means that Scorpius, that proud standout of the southern sky in July, is now tilting over and lying down in the southwest, preparing to bed down and drift off for the season.

■ Tonight the Moon hangs next to the Teapot's spout.

TUESDAY, SEPTEMBER 2

■ Now the Moon resides in or near the Teapot's handle. Covering the Moon with your fingertip helps reveal stars near it.

■ If you live in the world's mid-northern latitudes, look for bright Vega passing your zenith as twilight fades away now. Vega goes right through your zenith if you're at latitude 39° north: near Baltimore, Kansas City, Lake Tahoe, Sendai, Beijing, Ankara, Athens, Lisbon.

WEDNESDAY, SEPTEMBER 3

■ Titan, Saturn's largest moon, casts its shadow onto Saturn's face tonight. Every 15 years, around the time we see Saturn's rings edge on, Titan repeatedly crosses in front of Saturn from Earth's viewpoint — and, more visibly, casts its very tiny black shadow onto the planet. The current series of these events is nearing its end.

Tonight Titan's shadow transits the planet's high northern latitudes from 5:25 to 8:50 UT September 4th (UT date). In EDT that's tonight from 1:25 a.m. to 4:50 a.m. In PDT it's from 10:25 p.m. to 1:50 a.m.

Wherever you are Saturn is up almost all night now, though it's highest in the steadiest atmospheric seeing after midnight. So all of North and Central America again gets a chance at this event. See Bob King's Titan Shadow Transit Season Underway.

But if you're used to seeing shadows of Jupiter's moons on Jupiter, be warned: Saturn is twice as far away, and although Titan is large, it's not twice as large as Jupiter's moons.

THURSDAY, SEPTEMBER 4

■ How soon after sunset can you see the big Summer Triangle? As the very first stars come out. Vega, the Triangle's brightest star, is nearly at the zenith (for skywatchers at mid-northern latitudes). The next-brightest star of the Triangle is Altair, high in the southeast. Hint: The Moon this evening hangs lower in the southeast at dusk. Look for Altair halfway between it and Vega.

The last of the three Summer Triangle stars is Deneb, two fists east of Vega.

After dark, of course, they stand out prominently. I can even see them from downtown Boston. As night grows late the Triangle slides toward the west, a preview of what it will do in early evening through the fall.

FRIDAY, SEPTEMBER 5

■ The waxing gibbous Moon shines in the south-southeast this evening, on a line between Altair and Fomalhaut. Altair is the bright star three or four fists above the Moon and maybe somewhat to the right. Fomalhaut, the Autumn Star, rises a little after dark depending on your latitude.

Imagine a line from Altair down through the Moon and continuing on. The line will hit either Fomalhaut or the place on your horizon to watch for Fomalhaut to rise.

SATURDAY, SEPTEMBER 6

■ The bright Moon early this evening forms an isosceles triangle (two equal sides) with Saturn to its lower left and Fomalhaut the same distance down to its lower right. At the night advances, the triangle climbs higher while turning clockwise.

SUNDAY, SEPTEMBER 7

■ Full Moon (exactly full at 2:09 p.m. EDT). Saturn follows about 8° or 10° behind it across the sky tonight. Saturn is just two weeks from its own opposition.

■ With your naked eyes, what is the smallest surface feature that you can see on the Moon? Test your vision with the Lunar Eye Chart on pages 52 and 53 of the September Sky & Telescope. The 12 increasingly difficult test markings were worked out more than a century ago by Harvard astronomer W. H. Pickering.

■ A total eclipse of the Moon will occur for easternmost Africa, most of the Middle East and Asia, and the western half of Australia.

This Week's Planet Roundup

Mercury sinks down into the glow of sunrise this week. Jupiter and Venus high above it helpfully point down to its location. And at least Mercury is bright. It grows from magnitude –1.1 on Saturday morning August 30th to –1.5 a week later.

Venus and Jupiter shine in the east before and during dawn. They blaze at magnitudes –3.9 and –2.0, in Cancer and Gemini respectively. Jupiter is the top one.

The gap between them continues to widen by 1° per day: from 18° apart on Saturday August 30th to 25° a week later on September 6th. Both are about at their farthest from Earth, so don't expect much in a telescope.

Mars, a weak magnitude 1.6 in Virgo, still glimmers very low in the west during evening twilight. Binoculars will help. Mars sets shortly before twilight's end. It too is about at its farthest from Earth.

Don't confuse orange Mars with brighter, whiter, twinklier Spica to its left or upper left. Mars and Spica are 10° apart on Friday August 29th, narrowing to 5½° by Friday September 5th. Binoculars help.

Saturn (magnitude +0.7, in Pisces) rises due east in twilight. It's lower right of the Great Square of Pegasus, which stands on one corner diamond fashion.

But the best time to observe Saturn with a telescope is after midnight when it's high toward the south. We see Saturn's rings almost edge-on this year.

Uranus (magnitude 5.7, in Taurus near the Pleiades) rises around 10 or 11 p.m. and gets high in the east in the early morning hours. In a telescope it's a tiny but definitely non-stellar dot 3.6 arcseconds wide.

Neptune, a telescopic "star" at magnitude 7.8, lurks less than 2° north of Saturn. Use the finder chart for Neptune with respect to Saturn in the September Sky & Telescope, page 49. With a pencil, put a dot on the path of each of the two planets for your date. Neptune is just 2.4 arcseconds wide.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions and graphics that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is also known as UTC, GMT, or Z time.

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For a more detailed constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

For the attitude every amateur astronomer needs, read Jennifer Willis's Modest Expectations Give Rise to Delight.

Once you get a telescope, to put it to good use you'll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It's currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (with 201,000+ stars to magnitude 9.5 and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), and Uranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet (which many observers find more versatile) as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it's up to H.

Can computerized telescopes replace charts? Not for beginners I don't think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning how to explore the sky. As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand and a curious mind." Without these, "the sky never becomes a friendly place."

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye heavens above. It's free.

"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
            — Carl Sagan, 1996

"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
            — John Adams, 1770